1. Field of the Invention
The present invention relates to coating method and apparatus, a permanent magnet, and a manufacturing method thereof, and more particularly to a permanent magnet and a manufacturing method thereof in which the permanent magnet is manufactured by coating vaporizable metallic material including at least one of Dy and Tb on a surface of a magnet of Fe—B-rare earth elements, and then diffusing at least one of Dy and Tb into crystal grain boundary phases of a sintered magnet by heat treating the vaporizable metallic material at a predetermined temperature, as well as to coating method and apparatus suitable for coating vaporizable metallic material including at least one of Dy and Tb on the surface of the magnet.
2. Description of Background Art
A sintered magnet of Nd—Fe—B (a so-called “neodymium magnet”) has been used in various products e.g. motors for a hybrid vehicle and generators etc. recently since the neodymium magnet can be made of combination of elements Fe, Nd and B which are cheap and sufficiently and stably obtainable resources and also has high magnetic properties (its maximum energy product is 10 times that of ferritic magnet). On the other hand the sintered magnet of Nd—Fe—B has a problem that it is demagnetized by heat when it is heated beyond its predetermined temperature since its Curie temperature is low such as 300° C.
Accordingly when manufacturing the sintered magnet of Nd—Fe—B, since Dy and Tb have the magnetic anisotropy of 4 f-electron larger than that of Nd and have the negative Stevens factor similarly to that of Nd, it can be appreciated to add Dy or Tb to remarkably improve the magnetocrystalline anisotropy of the principal phase. However, since Dy and Tb take the ferrimagnetism structure in which Dy and Tb take a spin orientation opposite to that of Nd in the principal phase crystal lattice, it is caused a problem that the magnetic field strength, therefore the maximum energy product exhibiting the magnetic properties is greatly reduced.
For solving such a problem, it is proposed to firstly coat Dy or Tb on a whole surface of a sintered magnet of Nd—Fe—B having a predetermined configuration such as a rectangular parallelopiped at a predetermined coating thickness (thickness more than 3 μm determined based on a volume of the magnet) and then to uniformly diffusing Dy and Tb coated on the surface of the magnet into the crystal grain boundary phases of the magnet with carrying out heat treatment at a predetermined temperature (see non-patent document 1 mentioned below).
The permanent magnet manufactured according to this method has merits in that the coercive force generating mechanism of nucleation-type is reinforced by an effect that Dy and Tb diffused in the crystal grain boundary phases increase the magnetocrystalline anisotropy in each crystal grain surface and by the result of which the coercive force is remarkably improved almost without causing loss of the maximum energy product (for example, the non-patent document 1 discloses that it is possible to have a magnet having the coercive force of 23 K0e (3 MA/m) at the remanent magnetic flux density of 14.5 kG (1.45 T) and the maximum energy product of 50 MG0e (400 Kj/m3). When coating Dy or Tb on the surface of the sintered magnet of Nd—Fe—B, it can be appreciated to use the sputtering method that exhibits an excellent adhesion of Dy or Tb coating to a surface of sintered magnet.
Note: non-patent document 1; “Improvement of coercive on thin Nd2Fe14B sintered permanent magnets” (Park Ki Te, A doctor's thesis of Touhoku University, Mar. 23, 2000).